Answer is: 2) chlorine.
Fluorine (F) and chlorine (Cl) are halogen elements.
Halogen elements are in group 17: fluorine (F), chlorine (Cl), bromine (Br) and iodine (I). They are very reactive and easily form many compounds.
Both of them form diatomic covalent molecules (F₂, Cl₂).
Fluorine and chlorine are both in gaseous state.
Both molecules have single covalent bond and they are very reactive.
They have seven valence electrons.
They need to gain one electron to have electron cofiguration like next to it noble gas.
For example, fluorine has 9 electrons and it gain easily one electron in chemical reaction to have electron configuration like noble gas neon (Ne) with 10 electrons.
